Recruitment of cell types in the Drosophila retina is based on precursor cells sending, receiving and responding to positional cues. Previous work in this laboratory as well as elsewhere has established that hedgehog gene is a primary signal for initiating the wave of morphogenesis. Other genes, wingless and patched, are known act to in the same process. The finding that homologous genes may play similar roles in the vertebrate retina increase the significance of this work. The proposed work will extend the description of events at the morphogenic furrow. There are three specific aims. The first aim will examine the aspects of Hedgehog expression in the eye. Data suggesting that an element in the first intron is responsible for proper regulation of hedgehog gene in the retina. This will be investigated by isolating the element and investigating its ability to activate a reporter gene in the retina. A second goal is to use a sophisticated cell marker protocol to determine the competence of cells to respond to the Hedgehog signal. The second aim examines the role of pair-rule class of segmentation genes in the developing retina. Antibodies will be used to determine the sites of activity of these genes in the retina. These genes are identified by lethal mutations that will be analyzed as developmental lethal mutants. The third aim is to identify new genes that interact with hedgehog in eye development. Preliminary results establish the utility of a screen to look for genes that modify a weak hedgehog phenotype. Identified genes will be mapped and recessive phenotypes analyzed using genetic mosaics. Novel genes showing mutant phenotypes of interest will be subjected to molecular analysis.